Why don't we seem humans drifting into being sociopaths? E.g. starting as a normal, well adjusted human being and then becoming sociopaths as they get older?

That's an interesting question, partially because we'd want to copy that and implement it in AI. A large part of it seems to be social pressure, and lack of power: people must respond to social pressure, because they don't have the power to ignore it (a superintelligent AI would be very different, as would a superintelligent human). This is also connected with some evolutionary instincts, which cause us to behave in many ways as if we were in a tribal society with high costs to deviant behaviour - even if this is no longer the case.

The other main reason is evolution itself: very good at producing robustness, terrible at efficiency. If/when humans start self modifying freely, I'd start being worried about that tendency for them too...